Two small balls, each carrying a charge q are suspended by equal...

Suppose, $T$ be the tension in the spring $T$. Also in the satellite, two balls will be in a straight line. So, force acting on the balls $F=\frac{1}{4 \pi \varepsilon_0} \frac{q^2}{(2 l)^2}$ $\ldots$ (i) This force will be balanced by tension in the string. i.e., $T=F$ $\ldots$ (ii) Now, from Eqs. (i) and (ii), we get $T=\frac{1}{4 \pi \varepsilon_0} \frac{q^2}{4 l^2}$